1. Field of the Invention
This invention relates to a packing for use in a steel-pipe hydraulic testing apparatus, and more particularly to a packing for use in such a portion of the testing apparatus, which requires to maintain water-tightness of the pipe.
2. Description of the Prior Art
It has been a common practice that steel pipes such as casing pipes and the like are subjected to thread-cutting at their opposite ends and then to the subsequent hydraulic test, followed by storage. In this connection, the threaded opposite ends of a pipe are protected by using protectors or caps which are fitted on the aforesaid threaded ends of the pipe. Hitherto, upon hydraulic test, one end of a pipe is fitted in the head stock-head of a hydraulic testing apparatus, with the aforesaid protector or cap fitted on one threaded end of the pipe, while the other end of the pipe is fitted in the tail stock-head of the testing apparatus, with a protector or a cap removed from the other threaded end of the pipe. In this manner, the steel pipe is fixed in the hydraulic testing apparatus. Then, a pilot hydraulic pressure is applied to the outer periphery of an annular packing, which is located around the root portion of the threaded end of the pipe, so that the packing will be compressed radially, thereby bringing the inner peripheral surface of the packing in intimate contact with the outer periphery of the pipe. Then, the hydraulic pressure is applied to the interior or the inner surface of the pipe for intended testing.
However, the prior art testing apparatus suffers from shortcoming in that, upon testing, a protector or cap fitted on the other end of a pipe, which in turn is to be fitted in the tail stock-head of the testing apparatus, should be removed and hence many man hours are required for removal of the protector, so that the operational efficiency of the hydraulic test is remarkably lowered. For this reason, it has been desired to provide a testing apparatus which permits the testing of a steel pipe, without removing the protector or cap therefrom.
In this respect, there arises a problem that when a protector or cap is fitted on the end of a pipe, the outer diameter of the pipe is becomes too large to insert the aforesaid end of the pipe into the prior art packing. If there is provided a packing which permits the insertion of such an end of the pipe, there necessarily arises an increase in the clearance between the outer periphery of the pipe and the inner peripheral surface of the packing. This brings about accompanying problems. In other words, a pressure is applied to the inner peripheral surface of the packing along the length of the pipe towards its center portion, upon application of a hydraulic test pressure, so that such a portion of the packing which contacts a steel pipe will creep or yield towards the center portion of the pipe, thereby causing leakage of pressure water or breakage of the packing.
This is particularly true with the case where there is a considerable degree of clearance between the packing and the pipe. In addition, in the event of the failure or breakage of the packing, considerably many hours are required for replacement of the packing, with resulting lowered operational efficiency.
The aforesaid shortcomings or problems largely affect not only the efficiency of hydraulic test but also the accuracy of hydraulic test itself.